Switchgear
Low voltage switchgear
Main switchboards and power distribution assemblies up to 1000 V AC, sized from the rated current of the transformer that feeds them.
At a glance
- Standard
- IEC 61439-1 and IEC 61439-2power switchgear assemblies up to 1000 V AC or 1500 V DC
- Incomer
- sized from the transformer currentcommonly 630 A to 6300 A
- Devices
- air and moulded case circuit breakersIEC 60947-2
- Internal separation
- Forms of separationset by the continuity of service required
- Short circuit rating
- kA for a stated durationset by the transformer and the upstream network
A main low voltage switchboard is sized from the transformer that feeds it. The transformer's rated current sets the incomer and the busbar, and its impedance, together with the upstream network, sets the prospective fault level the board and its breakers must withstand and interrupt.
The assembly is designed and verified by its manufacturer to IEC 61439, which places the verification of temperature rise, short circuit withstand and dielectric properties on the original manufacturer and the assembly manufacturer. The internal separation between busbars, functional units and terminals decides how much of the board can stay energised while one part is worked on.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Rated current of the incomer | 630 A to 6300 A | The transformer rated current |
| Rated short time withstand current | kA for a stated duration | The prospective fault level |
| Form of internal separation | Form 1 to Form 4 as defined in IEC 61439-2 | The continuity of service required during maintenance |
| Incoming device | Air circuit breaker or moulded case circuit breaker | The current and the protection functions needed |
| Outgoing ways | Number, ratings and device types | The loads supplied |
| Busbar and connection | Cable or busbar trunking from the transformer | The current and the room layout |
| Metering and monitoring | Meters, power quality, communication | The owner's energy management |
| Degree of protection | IP rating | The room the board stands in |
Typical options are the ones buyers most often specify. They are not a list of what is available, which is confirmed per enquiry.
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 61439-1 | Low voltage switchgear and controlgear assemblies, general rules |
| IEC 61439-2 | Power switchgear and controlgear assemblies up to 1000 V AC or 1500 V DC |
| IEC 60947-2 | Low voltage circuit breakers up to 1000 V AC or 1500 V DC |
| IEC 60529 | Degrees of protection provided by enclosures |
The standard that applies is set by the specification and the destination market. Editions change, so the edition cited in a specification is confirmed in the quotation.
Documents normally requested
| Document | What it evidences |
|---|---|
| Technical datasheet and single line diagram | Ratings, panel functions and the arrangement offered |
| General arrangement drawing | Footprint, height, cable entry and floor fixings |
| Type test report | The design has passed the type tests of its standard, including internal arc where claimed |
| Routine test report | The individual assembly's tests before dispatch |
| Schematic and wiring diagrams | Control, protection and interlocking circuits |
| Operating and maintenance manual | Operation, interlocks and maintenance |
An internal arc classification is only as good as the type test behind it, and it applies to the tested configuration. Ask for the report that matches the arrangement offered.
What we need to quote accurately
| 01 | Incomer rating, or the transformer rating and secondary voltage that feed the board |
| 02 | Prospective fault level at the board, or the transformer impedance and upstream network data |
| 03 | Form of internal separation required |
| 04 | Schedule of outgoing ways with ratings and device types |
| 05 | Connection from the transformer: cable or busbar trunking |
| 06 | Metering, monitoring and communication requirements |
| 07 | IP rating and the room dimensions |
| 08 | Quantity, destination, required delivery date and acceptable condition |
Delivery and logistics
Distribution equipment is heavy, and a delivery date is only real once the site is ready for it. The dimensions and weight of the unit offered decide the vehicle, the lifting equipment and the route to the foundation, and they come from the manufacturer's drawing rather than from the rating.
Liquid immersed transformers are usually shipped filled, which affects transport rules and the handling on arrival. Anything crossing a border also carries customs documentation, and where the destination applies its own conformity or energy efficiency rules the paperwork has to match that market rather than the country of manufacture.
Lead times vary widely with rating, specification and manufacturer loading. We state a delivery basis in each quotation for the specific unit offered and do not publish a general lead time we cannot hold.
Common questions
What incomer rating does my transformer need?
Start from the transformer's rated current at the secondary voltage. Each distribution transformer rating page on this site states it at 400 V and 433 V together with the next standard device rating above it, which the designer then confirms against loading and discrimination.
Related
Request a quote for this equipment
Send the rating, the voltage and the destination, or submit the specification, drawing or nameplate. Anything missing is raised before it reaches a supplier.